Direct numerical simulations of head-on collision of evaporating droplets

Spray combustion is crucial in aero-engines and various industrial applications, with the dynamics of evaporating droplets being a critical phenomenon. This study employs direct numerical simulations to examine the head-on collision of evaporating droplets, utilizing the volume-of-fluid method to capture the gas–liquid interface while fully resolving the heat transfer across it. The effects of different evaporating conditions, characterized by varying ambient gas phase temperatures, on droplet dynamics are explored. The temporal evolution of kinetic energy, surface energy, and viscous dissipation is quantitatively analyzed. It is observed that kinetic energy decays more rapidly with higher temperatures, and viscous dissipation decreases with increasing gas phase temperature. In contrast to non-evaporating droplet collisions, the critical Weber number increases due to Stefan flow on the evaporating droplet surface, which impedes the collision process. Consequently, a semi-empirical model for the critical Weber number under evaporating conditions is developed, aiming to offer accurate predictions of droplet dynamics for realistic spray combustion simulations in aero-engines.